Catalyst for skeletal isomerization

ABSTRACT

The catalytic reforming of a feedstock which contains a derivative of cyclopentane or which contains organic compounds which are convertible to a derivative of cyclopentane is carried out in the presence of a hydrogel of zinc titanate and a suitable acidic material. Also, the attrition resistance of zinc titanate is improved by incorporating the zinc titanate into a hydrogel structure.

This application is a division of application Ser. No. 443,720, filedNov. 22, 1982, now U.S. Pat. No. 4,446,013.

This invention relates to a process for the skeletal isomerization ofderivatives of cyclopentane, and a catalyst therefor. This inventionalso relates to a method for improving the attrition resistance of azinc titanate catalyst.

Petroleum processing requires a number of separate process steps tochange the petroleum feed stock into desired products. An initialprocess step which is frequently utilized is reforming.

Reforming is the term which is utilized to refer to a number of processsteps which are all designed to increase the octane number of gasolinerange materials having a normal boiling range between about 50° C. andabout 200° C. (generally referred to as a naphtha feedstock). The mostimportant aspect of reforming is the dehydrogenation of cyclohexane andits derivatives to aromatics. Other aspects of reforming are thecyclization of paraffins to either cyclopentane and its derivatives orcyclohexane and its derivatives. Paraffins cyclized to derivatives ofcyclopentane are isomerized to cyclohexane and its derivatives forsubsequent aromatization.

Hydrogen must be added to the reforming process to prevent thederivatives of cyclopentane which are present in the naphtha feedstockor which are produced by the cyclization of paraffins from beingconverted to carbon which will very quickly foul the reforming catalyst.In the presence of hydrogen, derivatives of cyclopentane are isomerizedto cyclohexane and its derivatives. Cyclohexane and its derivatives maybe dehydrogenated to aromatics and the fouling of the catalyst issubstantially prevented.

U.S. Pat. No. 4,263,133 discloses that zinc titanate is effective as areforming catalyst. However, while zinc titanate is an excellentcatalyst for many of the process steps which are included in reforming,the zinc titanate catalyst of U.S. Pat. No. 4,263,133 exhibits littleactivity with respect to the isomerization of derivatives ofcyclopentane to cyclohexane and its derivatives. Since thisisomerization step is important in the reforming of feed stocks whichcontain derivatives of cyclopentane, it is an object of this inventionto improve the activity of the zinc titanate catalyst of U.S. Pat. No.4,263,133 for the skeletal isomerization of derivatives of cyclopentane.

The zinc titanate catalyst of U.S. Pat. No. 4,263,133 is regeneratedperiodically by contacting the zinc titanate catalyst with free oxygen.This regeneration requirement suggests that when the zinc titanatecatalyst is used as a reforming catalyst it could be advantageously usedin a moving bed or transfer line reactor. However, while the zinctitanate catalyst of U.S. Pat. No. 4,263,133 can be used in a moving bedor transfer line reactor, it would be desirable to improve the attritionresistance of the zinc titanate catalyst since an attrition resistantcatalyst is desirable for use in a moving bed or transfer line reactor.It is thus another object of this invention to provide a method forimproving the attrition resistance of the zinc titanate catalyst of U.S.Pat. No. 4,263,133.

In accordance with the present invention, a zinc titanate catalyst ismixed with a hydrosol of a suitable acidic material. A suitable base isthen added to the resulting mixture to form a hydrogel. The hydrogel isdried slowly and calcined to form what will be referred to as a zinctitanate hydrogel.

The zinc titanate hydrogel is utilized as a catalyst in a reformingprocess. The reforming process preferably has alternate reaction periodsand regeneration periods. The reforming process is carried out undersuitable conditions in the substantial absence of free oxygen. Hydrogenis added to the reforming process. The catalyst regeneration process iscarried out in the presence of a free oxygen containing gas to removecarbonaceous material which may have formed on the zinc titanatehydrogel during the reforming process. The use of the zinc titanatehydrogel results in an improved isomerization of derivatives ofcyclopentane to cyclohexane and its derivatives over that seen with thezinc titanate catalyst of U.S. Pat. No. 4,263,133 which has the effectof enhancing the octane yield from a naphtha feed stock. Also, the zinctitanate hydrogel exhibits an improved attrition resistance with respectto the zinc titanate catalyst of U.S. Pat. No. 4,263,133 which isadvantageous when using a moving bed or transfer line reactor.

Other objects and advantages of the invention will be apparent from theforegoing brief description of the invention and the appended claims, aswell as the detailed description of the invention which follows.

Any suitable reformable organic compound can be reformed in accordancewith the present invention. Organic compounds which are considered to beadvantageously and efficiently reformed in accordance with the processof this invention are the gasoline range materials having a normalboiling range between about 50° C. and about 205° C. The invention isparticularly directed to the reforming of gasoline range materials whichcontain derivatives of cyclopentane at some point in the reformingprocess.

The feed stock may contain sulfur compounds without impairing theactivity of the catalyst. However, sulfur will generally be converted tohydrogen sulfide at reforming conditions. Thus, it is preferable to usedesulfurized feed to obviate the need for removal of the hydrogensulfide downstream from the reformer.

The reforming catalyst employed in the process of the present inventionis zinc titanate in a hydrogel of a suitable acidic material. Ingeneral, the catalyst composition is prepared by first preparing zinctitanate which is then reduced to a small size. The resulting materialis mixed with a hydrosol of a suitable acidic material. A suitable baseis then added to the mixture to form a hydrogel. The resulting hydrogelis dried slowly and calcined to form the zinc titanate hydrogel catalystof the present invention.

The zinc titanate portion of the catalyst composition may be prepared byinitimately mixing suitable portions of zinc oxide and titanium dioxide,preferably in a liquid such as water, and calcining the mixture in thepresence of free oxygen at a temperature in the range of about 650° C.to about 1050° C., preferably in the range of about 675° C. to about975° C., to form zinc titanate. A calcining temperature in the range ofabout 800° C. to about 850° C. is most preferred because the surfacearea of the zinc titanate is maximized in this temperature range, thusproducing a more active zinc titanate. The titanium dioxide used inpreparing the zinc titanate preferably has extremely fine particle sizeto promote intimate mixing of the zinc oxide and titanium dioxide. Thisproduces a rapid reaction of the zinc oxide and titanium dioxide whichresults in a more active zinc titanate. Preferably the titanium dioxidehas an average particle size of less than 100 millimicrons and morepreferably less than 30 millimicrons. Flame hydrolyzed titanium dioxidehas extremely small particle size and is particularly preferred inpreparing the zinc titanate. The atomic ratio of zinc to titanium can beany suitable ratio. The atomic ratio of zinc to titanium will generallylie in the range of about 1:1 to about 3:1 and will preferably lie inthe range of about 1.8:1 to about 2.2:1 because the activity of the zinctitanate is greatest for atomic ratios of zinc to titanium in thisrange. The term "zinc titanate" is used regardless of the atomic ratioof zinc to titanium.

The zinc titanate portion of the catalyst composition may also beprepared by coprecipitation from aqueous solutions of a zinc compoundand a titanium compound. The aqueous solutions are mixed together andthe hydroxides are precipitated by the addition of ammonium hydroxide.The precipitate is then washed, dried and calcined, as described in thepreceding paragraph, to form zinc titanate. This method of preparationis less preferred than the mixing method because the zinc titanateprepared by the coprecipitation method is softer than the zinc titanateprepared by the mixing method.

The resulting zinc titanate is reduced to a suitable size for mixingwith a hydrosol of an acidic material by any suitable method such astreatment in an ultrasonic disrupter. The zinc titanate may be reducedto any suitable size with a particle size in the range of about 1 toabout 5 microns being preferred.

The resulting zinc titanate having a fine particle size is mixed with ahydrosol of a suitable acidic carrier. Any suitable acidic carrier suchas an alumina, a silica-alumina or a zeolite material may be utilized.An alumina is preferred because it forms a well dispersed hydrosolphase. Alumina hydrate is particularly preferred because a hydrosol ofalumina hydrate is readily converted to a hydrogel and then to the oxidephase after calcination.

After the zinc titanate has been thoroughly mixed into the hydrosol, asuitable base is added to convert the hydrosol to a hydrogel. Anysuitable base such as alkali metal hydroxides, ammonium hydroxide, orurea may be utilized. Ammonium hydroxide is the preferred base becauseit does not have any metallic component that would remain in thehydrogel.

The resulting hydrogel is dried slowly so that water will not be removedso rapidly that the hydrogel structure will collapse which would resultin excessive loss of pore volume and surface area of the finished zinctitanate hydrogel. Any suitable drying time can be utilized which doesnot result in too rapid removal of water. Preferably, the drying time isin the range of about 8 hours to about 24 hours.

Any suitable temperature can be utilized for the drying of the zinctitanate hydrogel but again the temperature should be such that toorapid a removal of water does not result. The temperature is preferablyin the range of about 35° C. to about 150° C. The most preferred dryingcondition is to start the drying process at about 80° C. and increasethe temperature slowly to about 120° C. during the drying time.

After the zinc titanate hydrogel has been dried, the zinc titanatehydrogel is calcined in the presence of free oxygen. Any suitable freeoxygen-containing gas may be utilized with air being preferred becauseof its availability. Also, any suitable time and temperature for thecalcining may be utilized with a preferred time being about two hoursand a preferred temperature being in the range of about 425° C. to about650° C. and more preferably in the range of about 480° C. to about 600°C. Although the dried zinc titanate hydrogel can be placed directly intoa preheated furnace or kiln for calcining, it is preferable for thecatalyst to attain its final temperature during a heating period ofabout two hours.

The finished catalyst composition can contain any suitable weightpercent of zinc titanate. In general, the amount of zinc titanate in thefinished catalyst composition will be in the range of from about 10weight percent to about 50 weight percent based on the total weight ofthe catalyst composition and will more preferably be in the range offrom about 20 weight percent to about 40 weight percent based on theweight of the total catalyst composition.

The process of this invention can be carried out by means of anyapparatus whereby there is achieved an ultimate contact of the catalystwith the organic compound to be reformed and thereafter of the catalystwith the oxygen-containing gas. The process is in no way limited to theuse of a particular apparatus. The process of this invention can becarried out using a fixed catalyst bed, fluidized catalyst bed or movingcatalyst bed. Because of the attrition resistance of the catalyst andthe need for periodic regeneration, the moving catalyst bed is presentlypreferred in the process of the present invention.

In order to avoid any casual mixing of the organic feed and the oxygencontaining fluid utilized in the regeneration step, provision ispreferably made for terminating the flow of feed to the reactor andinjecting an inert purging fluid such as nitrogen or carbon dioxide. Anypurge time suitable to prevent mixing of the organic feed and the oxygencontaining fluid can be utilized. The purge duration will generallyrange from about 1 minute to about 10 minutes and will more preferablyrange from about 3 minutes to about 6 minutes. Any suitable flow rate ofthe purge gas may be utilized. Presently preferred is a purge fluid flowrate in the range of about 800 GHSV to about 1200 GHSV.

Any suitable temperature for reforming organic compounds over the zinctitanate hydrogel can be utilized. The reforming temperature willgenerally be in the range of about 427° to about 593° C. and will morepreferably be in the range of about 510° to about 566° C.

Any suitable pressure for the reforming of the organic feedstock overthe zinc titanate hydrogel can be utilized. In general, the pressurewill be in the range of about 50 to about 700 psig and will morepreferably be in the range of about 150 to about 350 psig. The pressurewill be in terms of total system pressure where total system pressure isdefined as the sum of the partial pressures of the organic feedstock,the hydrogen added to the process, and the hydrogen produced in theprocess.

Any quantity of hydrogen suitable for substantially preventing theformation of coke can be added to the reforming process. The quantity ofhydrogen added will generally be in the range of about 0.5 to about 20moles per mole of hydrocarbon feed and will more preferably be in therange of about 2 to about 10 moles of hydrogen per mole of feedstock.

Any suitable residence time for the organic feedstock in the presence ofthe zinc titanate hydrogel can be utilized. In general, the residencetime in terms of the volume of liquid feedstock per unit volume ofcatalyst per hour (LHSV) will be in the range of about 0.1 to about 10and will more preferably be in the range of about 0.5 to about 5.

Any suitable time for the regeneration of the reforming catalyst can beutilized. The time for the regeneration of the catalyst will generallyrange from about 5 minutes to about 60 minutes and will more preferablyrange from about 10 minutes to about 30 minutes. The regenerationeffluent should be substantially free of carbon dioxide at the end ofthe regeneration period.

The amount of oxygen, from any source, supplied during the regenerationstep will be at least the amount sufficient to remove substantially allcarbonaceous materials from the catalyst. The regeneration step can beconducted at the same temperature and pressure recited for the reformingstep although somewhat higher temperatures can be used, if desired.

Catalysis of reforming reactions with the zinc titanate hydrogel is mosteffective with the use of relatively short process periods withintervening periods of oxidative regeneration. The duration of thereforming process period will generally be in the range of about 1minute to about 4 hours with a duration of about 5 minutes to about 60minutes being preferred.

The operating cycle for the reforming process will generally include thesuccessive steps of:

(1) contacting the organic feed with the catalyst to thereby reform theorganic feed;

(2) terminating the flow of the organic feed to the reactor;

(3) optionally, purging the catalyst with an inert fluid;

(4) contacting the catalyst with free oxygen to regenerate the catalyst;

(5) terminating the flow of free oxygen to the reactor; and

(6) optionally, purging the thus regenerated catalyst with an inertfluid before repeating step (1).

The following examples are presented in further illustration of theinvention.

EXAMPLE 1

Zinc titanate was prepared by mixing Mallinckrodt powdered zinc oxideand of Cab-O-Ti titanium dioxide (flame hydrolyzed) by slurrying in 150ml of water in a blender for 5 minutes. The ratio of zinc oxide totitanium dioxide used was such as to give an atomic ratio ofzinc:titanium in the finished preparation of 1.8:1. The resulting slurrywas dried in an oven at 105° C. and then calcined in air for three hoursat 816° C. After cooling, the thus calcined material was crushed andscreened, and a -16+40 mesh fraction was reserved for testing. Thispreparation is the same as the preparation of the zinc titanate asdescribed in Example 1 of U.S. Pat. No. 4,263,133. A portion of the thusprepared zinc titanate was utilized as the control catalyst.

81.0 grams of the thus prepared powdered zinc titanate was slurried into500 mL of water and treated with the transducer of an ultrasonic celldisrupter at high power for about 10 minutes to reduce the particle sizeof the zinc titanate to about 2-10 microns. The resulting slurry wascombined with a suspension of 189.1 grams of alpha alumina monohydrateand about 900 mL of water. Sufficient nitric acid was added to theresulting mixture to lower the pH of the resulting mixture from about7.6 to about 3.0 to produce the hydrosol. 10 mL of concentrated ammoniumhydroxide was then added to the hydrosol to produce a hydrogel. Thehydrogel was then dried in an oven for 18 hours at 82° C. and then thetemperature was increased to 149° C. for 2 more hours. The thru driedhydrogel was then calcined in air in a furnace which was heated to 648°C. during 2 hours and then held at that temperature for 2 hours. Theresulting zinc titanate hydrogel contained 35.5 weight percent zinctitanate based on the weight of the total hydrogel. The hydrogel wascrushed and screened and a -16+40 mesh fraction was reserved fortesting.

The zinc titanate catalyst prepared in accordance with the procedure ofU.S. Pat. No. 4,263,133 and the zinc titanate hydrogel were used in runsto reform methylcyclopentane. The desired reaction was to isomerizemethylcyclopentane to cyclohexane and then dehydrogenate the cyclohexaneto benzene. Runs were made using 25 mL of the -16+40 mesh catalyst mixedwith an equal volume of quartz chips. The catalyst mixed with quartzchips was placed in a stainless steel reactor mounted vertically in atemperature controlled electric furnace. The feed passed downflowthrough the reactor and the resulting liquid products were collected forsubsequent GLC analyses. Analyses of gaseous products (H₂ to C₅) wasbased on snap samples taken periodically into a gas chromatograph. Allruns were made at 538° C., 300 psig, 1.0 LHSV and ahydrogen:methylcyclopentane feed mole ratio of four. Results of runswith the two catalysts are set forth in Table 1.

                  TABLE 1                                                         ______________________________________                                                               ZINC TITANATE                                                     ZINC TITANATE                                                                             HYDROGEL                                               ______________________________________                                        Time on stream (hrs.)                                                                      1        15       106                                            Methylcyclopentane                                                                         18.5     13.0     78.0/80.9/64.8*                                Conversion (%)                                                                Selectivity to                                                                             32.2     21.8     37.8/46.0/41.1*                                Benzene (%)                                                                   ______________________________________                                         *Initial/Maximum/Final                                                   

Referring now to Table 1, although the method of reporting resultsdiffers, it is apparent that after 15 hours the zinc titanate catalysthas already lost an appreciable fraction of its activity which, at best,was much less than the zinc titanate hydrogel had during a 106 hour run.Regeneration was not used in either of the runs of Table 1.

EXAMPLE 2

Fifty gram portions of a -80+200 mesh fraction of the two catalyst ofExample 1 were fluidized with air in a cylindrical reactor for 44 hours.Fines smaller than 200 mesh are entrained in the air and caught in aseparate vessel for measurement during the test. Results of theattrition test show that the attrition rate (weight loss) is first orderand can be characterized by a first order rate constant. When subjectedto the attrition test, the rate constant for zinc titanate was about 0.2hr.⁻¹ and for the zinc titanate hydrogel it was about 0.0118 hr.⁻¹. Forcomparison, a commercial fluid cracking catalyst had a rate constant of0.0066 hr.⁻¹ when subjected to the same test.

It can be seen from the attrition test that the zinc titanate hydrogelhas a substantially higher attrition resistance than the zinc titanateof U.S. Pat. No. 4,263,133.

Reasonable variations and modifications are possible within the scope ofthe disclosure and the appended claims to the invention.

That which is claimed is:
 1. A catalyst composition comprising ahydrogel of zinc titanate and an acidic carrier.
 2. A catalystcomposition in accordance with claim 1 wherein the concentration of zinctitanate in said hydrogel is in the range of about 10 to about 50 weightpercent based on the weight of the hydrogel.
 3. A catalyst compositionin accordance with claim 1 wherein the concentration of zinc titanate insaid hydrogel is in the range of about 20 to about 40 weight percentbased on the weight of the hydrogel.
 4. A catalyst composition inaccordance with claim 1 wherein said acidic carrier is alumina.
 5. Acatalyst composition in accordance with claim 1 wherein said zinctitanate is prepared by calcining a mixture of zinc oxide and titaniumdioxide in the presence of free oxygen at a temperature in the range ofabout 650° C. to about 1050° C.
 6. A catalyst composition in accordancewith claim 5 wherein the atomic ratio of zinc to titanium is in therange of about 1:1 to about 3:1.
 7. A catalyst composition in accordancewith claim 5 wherein the atomic ratio of zinc to titanium is in therange of about 1.8:1 to about 2.2:1.
 8. A catalyst composition inaccordance with claim 1 wherein said hydrogel is formed by mixingpowdered zinc titanate with a hydrosol of alumina hydrate to form a zinctitanate/alumina hydrosol, adding ammonium hydroxide to convert saidhydrosol to a hydrogel and drying and calcining said hydrogel.
 9. Acatalyst composition in accordance with claim 8 wherein said hydrogel isdried for a time in the range of about 8 to about 24 hours and at atemperature in the range of about 35° C. to about 150° C.
 10. A catalystcomposition in accordance with claim 9 wherein the dried hydrogel iscalcined in the presence of free oxygen at a temperature in the range ofabout 425° C. to about 650° C. for a time of about 2 hours.